XITRON XT2640 - PWM Generator Efficiency Measurements

XT2640OperatingManual 13July2016 Page80of187

16.3.2.4 HARMONICSSETTING
Ifharmonicsmeasurementsarenotrequiredthenthisshouldbesettoeither0or1(ifsetto1thenthevectorsandcycleview
screensareavailable,otherwisetheyarenot).
Otherwise,thissettingdependsontheBANDWIDTHsettingmethodselected.Generally,becauseofthepresenceofthePWMcarrier
signal,measurementofmorethanafewharmonicsisinappropriateintheseapplications.
1.
BANDWIDTHsettoUNFILTERED.TheXT2640appliessufficientbandwidthrestrictionsonlytoharmonicsmeasurements
inthiscasesoitisnecessarytoensurethatharmonicmeasurementsdonotincludeanysignificantartifactsofthePWM
carrierfrequency.Youshouldcomputethehighestrequiredharmonichavingafrequencyof¼ofthePWMcarrier
frequencyandenterthatnumber(orless)fortheHARMONICSsetting.Ifthedriveissubsequentlyoperatedatadifferent
modulationfrequencythenthissettingmayneedtobealtered.Forexample,ifthemodulationfrequencyis50Hzandthe
PWMcarrierfrequencyis5kHzthenthehighestrecommendedHARMONICSsettingis(1/4*5000/50)=25.
2.
BANDWIDTHsettoUSER.InthiscasethevaluesetforHARMONICSselectsthehighestlimitforthenumberofavailable
harmonicsbuttheXT2640willalsoautomaticallyanddynamicallylimitittotheharmonichavingafrequencyof½ofthe
BANDWIDTHfrequencysetting.Sointhiscasethissettingonlysetsamaximumlimittothenumberofavailable
harmonics,typicallytheactualnumberislimitedbytheBANDWIDTHsetting.
3.
BANDWIDTHsettoAUTO‐TRACK.InthiscasetheXT2640willautomaticallylimitthebandwidthto3timesthefrequency
ofthehighestharmonicsetbytheHARMONICSsetting.YoushouldsetaHARMONICSsettingoflessthanPWMcarrier
frequency/(6*highestmodulationfrequency).Forexample,ifthehighestexpectedmodulationfrequencyis50Hzandthe
PWMcarrierfrequencyis5kHzthenthehighestrecommendedHARMONICSsettingis(5000/(6*50))=16.
Note:
Generallyeithernoharmonicsmeasurementsareneeded(sosetHARMONICSto0or1),oronlyafewhavesignificancetoyou
(sosetHARMONICStothelowestnumberpossible).
TheHARMONICSsettinghasnoeffectonnon‐harmonicmeasurements(e.g.RMSvoltageandcurrent,andWatts,VA,VAR,and
PF).
SignalscapturedusingtheCYCLEVIEWscreenarealsoaffectedbythischoice,butsignalscapturedbytheSCOPEVIEWscreen
arenot.
16.3.2.5 RESPONSESETTING
Becauseofthevariousasynchronoussignalcontentsandalsobecauseoftenthemeasurementsbeingmadearewithinanoverall
controlloop(e.g.motorspeedcontrol),thesesignalsoftenhaveconsiderablevariabilitysotheuseofresult“smoothing”is
recommended.ThisisselectedbyyourchoicefortheRESPONSEsettingandMEDIUMistherecommendedchoiceinmostPWM
applications.
Note:
Thissettingappliestoallmeasurementresults.
OfteninPWMapplicationsharmonicresultsrequiremoresmoothingthannon‐harmonicresultsbecauseoftheinter‐
harmonicandsub‐harmonicsignalcontentpresentinthesesignalscausedbytheasynchronousnatureofthecarrierand
modulationfrequencies,inthosecasesitisrecommendedtochangetheRESPONSEsettingaccordingtowhichresultsyou
wishtoobtainatthattime.Changingthissettingdoesnot“restart”thesmoothingbutcontinuesit,sochangingtheRESPONSE
settingwhilethesignalsarepresentisrecommendedtoavoidunnecessarilylongsettlingtimeswhenalongRESPONSE
settingisselected.
ItisgenerallybettertosmoothresultsbyapplyingalongerRESPONSEsettingthanselectingalongerLF/PERIODsettingas
theRESPONSEsmoothingisamulti‐ordersmoothingfilterwhereastheeffectofthemeasurementperiodistheequivalentofa
singleorderfilterandalsodoesnotapplycontinuousfilteringsohaslesseffect.
16.3.3 PWM GENERATOREFFICIENCYMEASUREMENTS
InsomeapplicationsitmaybedesiredtomeasureboththeoutputofaPWMpowergeneratorandalsothesupplytoit,e.g.forpower
generatorefficiencymeasurements.ThisisachievedbyconfiguringthetwomeasurementsintwodifferentVPAsinthesame
XT2640asfollows–
1.
IftherewillbesignificantchangestothelevelsorsignalswhichrequiretrackingforefficiencyresultsandthesupplyisDC
whichcontainsrippleatthemodulationfrequencyofthePWMgenerator(orlittlerippleatanyfrequency)andallchannels
areWtypechannelsorallarenotWtypechannels.
 TheMEASMODEshouldbesettoMULTIVPA.
 ThePWMgeneratoroutputVPAshouldbeconfiguredasVPA1.
 TheDCsupplyVPAshouldbeconfiguredasVPA2andDCmeasurements(FUND=NONEandCOUPLING=DCONLY).
 TheLF/PERIODsettingoftheDCVPA(VPA2)shouldbesetto“VPA1”.
 UsethesameRESPONSEsettinginbothVPAs.
InthismannertheXT2640willmeasuretheDCsupplyexactlysynchronouslywiththemeasurementsofthePWM
generatoroutput,andsowillrejecttheripplecontentandalsowillaccuratelytrackchangesinefficiencycausedbychanges
inthesignals.
2.
Sameasoption1abovebutthePWMmeasurementchannelsandtheDCmeasurementchannelsarenotofthesametype.
 TheMEASMODEshouldbesettoSYNCVPA.
 BothsetsofmeasurementsshouldbeconfiguredinseparateVPAs.AnyVPAcanbeusedforeithermeasurementand
bothareindependentlyconfigured.